The present invention relates to a process for the simultaneous production of 1,2- and 1,3-propanediol from one raw material, namely glycerol, wherein the first step is a dehydration of glycerol.
1,2-propanediol is a commercially produced product with a broad spectrum of applications and 1,3-propanediol is gaining importance as a structural unit for polyesters. Various processes are known for the production of 1,2- and 1,3-propanediol. 1,2-propanediol is obtained for example by hydrolysis of propylene oxide. 1,3-propanediol is obtained in general by hydration of acrolein on an acidic catalyst to produce 3-hydroxypropionaldehyde and then catalytic hydration of the 3-hydroxypropionaldehyde. With regard to the production of 1,3-propanediol from acrolein, reference is made for example to the processes described in the following documents: DE-A 39 26 136, DE-A 40 38 192, and German Patent Applications P 41 38 982.4, P 42 18 282.4 and P 41 38 981.6.
Only a few processes have become known whereby 1,2- and 1,3-propanediol are produced simultaneously from one raw material: 1,3- and 1,2-propanediol can be produced by reaction of glycerol with carbon monoxide and hydrogen in an organic solvent in the presence of a homogeneous catalyst system consisting of, for example, tungstic acid and a rhodium compound (see U.S. Pat. No. 4,642,394). A disadvantage of this process is the low yields of 1,2- and 1,3-propanediol, which in each case scarcely exceeds 20%; moreover, glycerol must be reacted in solution in an amine or amide, so that aqueous glycerol solutions cannot be used.
1,3-propanediol can be produced by fermentation from glycerol by Clostridium butyricum (see B. Gunzel et al., Applied Microbiology and Biotechnology, Springer Verlag 1991, pages 289-294). Although this method leads to 1,3-propanediol in moderate yields (ca. 60%), it must not be disregarded that the space-time yield of 1,3-propanediol in this fermentation is very low, namely 2.3 to 2.9 g.multidot.1.sup.-1 .multidot.h.sup.-1. The concentration of glycerol (about 5 to 6 g/l) in the solution to be fermented must be kept low since otherwise the growth of the cultures used is inhibited; the recovery of the 1,3-propanediol from the very dilute fermentation solutions is therefore energy-intensive. 1,2-propanediol is not formed.
According to another microbiological process (Environ. Microbiol. (1983), volume 46 (1), pages 62-67; Chem. Abstr. 99 (13): 103663s), glycerol can be converted by means of Klebsiella pneumoniae NRRL B-199 in 55% yield to 3-hydroxypropionaldehyde, the hydration product of acrolein, which can be converted in a known way to 1,3-propanediol. The fermentation is carried out using about 3% glycerol solutions and requires the presence of semicarbazide hydrochloride, which must be recovered again. The space-time yield of this process is low; moreover, the total process cost is high. Apparently no hydroxyacetone, which could be converted into 1,2-propanediol, is formed.
The formation of acrolein from glycerol, for example, has been studied in the gas phase under conditions of destructive gas chromatography (Ishikawa Koichi et al., Bunseki Kagaku 32 (10) E 321-E 325), wherein a very dilute aqueous solution of glycerol (1.5-150 mg/l) is fed at 260.degree. to 300.degree. C. in pulsed form over a gas chromatography (Poropak R) column coated with 10 to 30% KHSO.sub.4. A man skilled in the art receives no inducement from this document to turn the analytical method into the basis of a manufacturing process for the production of 1,2- and 1,3-propanediol from glycerol since only acrolein is named as a dehydration product and, moreover, the extreme dilution creates conditions which are completely different from those necessary in manufacturing processes in order to achieve a satisfactory space-time yield and catalyst life.
A process for the production of acrolein from glycerol is known from FR 695 931, wherein glycerol vapor is fed at above 300.degree. C., especially 400.degree. to 420.degree. C., over a fixed-bed catalyst. Salts of tribasic acids or mixtures of such salts, which can be present on a support, are claimed as catalyst; as shown in the examples, pumice coated with 1% lithium phosphate or with 1% iron phosphate is used. In this document, as shown in the examples, the acrolein yield is reported to be 75% or 80%. Advice to use the reaction mixture of the dehydration for the production of 1,2- and 1,3-propanediol cannot be found in this document. We have duplicated the process of FR 695 931 and in doing so established that under the reaction conditions tested the reported yields could not be obtained either with lithium phosphate or with iron phosphate; as the comparative examples show, the yield of acrolein at 300.degree. C. was only about 1 to 3% and at 400.degree. C. was 30 to 35%.